Direct Light-Driven Water Oxidation by a Ladder-Type Conjugated Polymer Photoanode

[Image: see text] A conjugated polymer known for high stability (poly[benzimidazobenzophenanthroline], coded as BBL) is examined as a photoanode for direct solar water oxidation. In aqueous electrolyte with a sacrificial hole acceptor (SO(3)(2–)), photoelectrodes show a morphology-dependent performance. Films prepared by a dispersion-spray method with a nanostructured surface (feature size of ∼20 nm) gave photocurrents up to 0.23 ± 0.02 mA cm(–2) at 1.23 V(RHE) under standard simulated solar illumination. Electrochemical impedance spectroscopy reveals a constant flat-band potential over a wide pH range at +0.31 V(NHE). The solar water oxidation photocurrent with bare BBL electrodes is found to increase with increasing pH, and no evidence of semiconductor oxidation was observed over a 30 min testing time. Characterization of the photo-oxidation reaction suggests H(2)O(2) or •OH production with the bare film, while functionalization of the interface with 1 nm of TiO(2) followed by a nickel–cobalt catalyst gave solar photocurrents of 20–30 μA cm(–2), corresponding with O(2) evolution. Limitations to photocurrent production are discussed.